In many cellular communications systems, the access to radio resources is controlled by the radio network. When a wireless transmit/receive unit (WTRU) has data to transmit to the network, it acquires radio resource access before transmitting its data payload. To achieve this in a 3rd Generation Partnership Project (3GPP) network, for example, a WTRU must gain access to the random access channel (RACH). Access to the RACH is contentious and there are mechanisms to reduce the probability of collision, that is, when two WTRUs are accessing the resource simultaneously.
Procedures for random access include a preamble phase with power ramp-up followed by channel acquisition information and message transmission. Because of the contentious nature of the RACH, to avoid WTRUs holding the shared radio resource for a long time, and because there is no power control, relatively short message payloads are transmitted on the RACH, leading to a relatively small data rate. Therefore, the RACH is generally used for the transmission of short control messages. Typically, WTRUs demanding larger data rates would be configured by the network to use dedicated resources.
While the data rate provided by the RACH is sufficient for the transmission of short control messages typical of networks supporting mostly speech communications, it is inefficient for the transmission of data messages associated with non-real-time data services, such as internet browsing, e-mail, and the like. For these data services, the traffic is bursty by nature and long periods of inactivity may exist between successive transmissions. For some applications requiring frequent transmission of keep-alive messages, for example, this may result in an inefficient utilization of dedicated resources. Therefore, it may be advantageous for the network to use shared resources for data transmission instead. The difficulty however, resides in the low data rate offered by the existing RACH.
FIG. 1 shows RACH access with an enhanced dedicated channel (E-DCH) 100 in accordance with the prior art. A RACH access with E-DCH 100, hereafter “E-RACH”, may include a RACH preamble phase 102, initial resource assignment 104, collision detection and resolution 106, an E-RACH message part 108, and release of resources 110 or transition to other state. It would be desirable to have a set of mechanisms for efficient use of the E-DCH on the E-RACH.